Well, perhaps a plotline where Harry discovers his Sans powers gradually. At first, he might be confused by these new abilities that seem so different from magic. He could start by accidentally using them in small ways, like making short 'teleports' in the Gryffindor common room when he's startled. Then, as he learns more about his powers, he uses them to help his friends, like saving Ron from a dangerous spell by quickly getting in between them with his super speed.
One possible plotline could be Harry using his Sans powers to avoid danger in the wizarding world. For example, he might use teleportation abilities similar to Sans to quickly escape from Death Eaters. Another could be him using his powers in Hogwarts challenges, like getting through mazes or solving puzzles with his special skills.
Harry might gain the ability to dodge attacks more easily. Sans has a certain 'instinct' for avoiding harm, and if Harry had this, it would be much harder for his enemies to land a hit on him. This would be really useful in duels, especially against powerful dark wizards. It could also make his Quidditch playing even more amazing as he could dodge bludgers effortlessly.
One interesting plotline could be Naruto having the power to control time. He could use this to prevent tragedies in the past, like the death of his parents. Another could be him having the ability to communicate with all animals, leading to new alliances and strategies in battles.
In some fanfictions, the OC with Sans' powers may find themselves in a world where they have to compete in a tournament. They use Sans' powers like his blue attack (the ability to make objects heavier) to gain an advantage over their opponents.
One plotline could be how the other characters in the story react to Sans being sick. For example, Papyrus might be overly worried and try all sorts of crazy remedies. Another could be Sans trying to hide his sickness because he doesn't want to be a burden.
Obviously, he'll interact with his main friends like Ron and Hermione. Ron might be both amazed and a bit jealous of Harry's new Sans powers at first. Hermione would probably be very curious and start researching to figure out where these powers came from. Harry might also interact with Dumbledore. Dumbledore would be intrigued and might offer some guidance on how to control and use these powers for good.
One common plotline is the exploration of their complex relationship. Sans, being a laid - back yet perceptive character, and Flowey, with his twisted nature, often find themselves in situations where they have to re - evaluate their views of each other. For example, they might team up against a greater threat in the Underground, which forces them to trust one another in a way they hadn't before.
Maybe it's about the characters from Undertale trying to understand Error Sans. Error Sans is a complex character with his own motives and backstory. In the fanfiction, the Undertale characters could be trying to figure out why he is causing disruptions and if there's a way to coexist with him. This could involve a lot of character development and exploration of different moral stances.
One cool power often seen in such fanfiction is teleportation. This allows characters to quickly move from one place to another, escaping danger or arriving at crucial moments just in time. There are also powers related to healing, where a character has an extraordinary ability to cure any injury or illness, which can be very useful in the often - dangerous wizarding world.
In some fanfictions, the Horntail and Harry might have a telepathic connection. This allows Harry to understand the dragon's thoughts and motives, and they work together to uncover secrets in the wizarding world. For example, they might find a hidden chamber that holds a powerful magic item that could change the course of the war against Voldemort.
One interesting plotline could be the little sister discovering she has her own unique magical abilities that are different from Harry's. For example, she might be able to communicate with magical creatures in a way no one else can.